1. Field of the Invention
The present invention relates to a structured combustion chamber for use in an engine.
2. Description of the Related Art
So far, in an engine mounted on an automobile, there has been known a mechanism which can vary a timing of lift (that is, phase based on rotation of a crankshaft) or quantity of lift of an intake valve or exhaust valve. This mechanism, which has already been put to practical use, is referred to as a valve operating mechanism or variable valve lift mechanism and is designed to improve the fuel consumption in a low rotation region while securing the engine output in a high rotation region.
As a document describing one example of a technology related to this valve operating mechanism, there is a technique disclosed in Japanese Patent Laid-Open No. 2004-293483 (patent document 1). This patent document 1 discloses a technique capable of varying the quantity of lift of an intake valve in two steps.
Meanwhile, FIG. 5 of this patent document 1 shows the formation of a wall portion, designated at reference numeral 45a, thereby producing a tumble flow in a combustion chamber when an intake valve is driven by a low lift cam.
In addition, this patent document 1 makes a disclosure to the effect of setting a height of the wall portion for the purpose of enhancing the suction flow in the case of the valve operation by the low lift cam. However, the formation of the wall portion based on such a consideration counteracts the suction flow into the combustion chamber, which additionally creates a problem of holding down the torque outputted from the engine.
On the other hand, in recent years, there has been developed a mechanism (so-called continuous variable valve lift mechanism) capable of continuously changing the quantity of lift of an intake valve or exhaust valve and being put into practice.
The employment of this continuous variable valve lift mechanism can change a quantity of lift of an intake valve continuously so as to freely vary the quantity of suction into the engine and, in a case in which the lift quantity of the intake valve is designed to vary according to the load needed, the reduction of fuel consumption becomes feasible by finely adjusting the quantity of suction.
Furthermore, in the continuous variable valve lift mechanism, the realization of delicate suction quantity control requires securing the performance in a high valve lift condition while enhancing the suction flow in a low valve lift condition.
Accordingly, in a case in which a wall portion is formed for the purpose of enhancing the suction flow in the case of the valve driving by the low lift cam as written in the patent document 1, no consideration is given to the engine performance in a high valve lift condition, which leads to considerably hindering the suction flow to the combustion chamber.
In particular, in the continuous variable valve lift mechanism, the maximum quantity of lift of the intake valve denotes the maximum acceleration pedal depressing quantity and signifies the requirement for the engine to produce the maximum torque output.
Therefore, in such a continuous variable valve lift mechanism, the formation of a wall portion disclosed in the patent document 1 extremely degrades the full-opening performance of the engine.